Electric blasting initiator



g- 20, 1940- c. R. JOHNSON ET AL 2,212,474,

ELECTRIC BLASTING INITIATOR Filed Dec. 24, 1937 659/465 1?. Job/x901 Hakim R jv d yy INVENTORS A 77 OR/VE Y Patented Aug. 20, 1940 v I 2,212,474

UNl'iED s'mrss PATENT or ies ELECTRIC BLASTING INITIATOR Charles B. Johnson, West Chester, Pa., and Roland R. Nydegger, Wilmington, Del., assignors to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware Application December 24, 1937, Serial No. 181,644

-7 Claims. (Cl. 102-10) The present invention relates to electric blastvention for the purpose of forming a water-proof s initiators a d m pa i ular y to a ve closure by crimping the shell on the blasting and improved method for the manufacture of iti t r into the rubber-like plug. water impervious electric blasting initiators. The reduced extension beyond the base of the AS is Well known. the Usual procedure for plug and integral therewith may take any shape manufacture of electric blasting initiators comprovided that it has a decreased area of crossp i embedding h l wir i a h rd cast section with respect to that of the body of the p u of Sulfur-Containing material and SHbSeplug of which it is an integral part, and surrounds quently Sealing this t into place in a loaded and closely adheres to the leg wires. For ex- 10 shell by means of thermopl stic Wa r-pr ample the extension may be cylindrical in shape, 10 compositions or Similar Sealing meenS- Such e or it may take the form of a pyramid truncated p du e is t ad p a t a mechanical cone, wedge, or the like. It may be in one piece method of a m y, but includes several or in two separate portions, one surrounding each plicated and undesirable hand operations, inleg wire, Preferably, however, we employ an volving both molten materialsand loaded shells. extension so constructed t t th ratio of th 15 Fu h u t he thermoplastic nature of area of cross-section of said extension to the t e Sea compo s q ed, the resulting combined area of cross-section of the leg wires assembly fails to provide adequate moisture prois relatively small. We prefer to employ an extec ion for th plo iv charge under varying tension from s to of an inch in thickness,

Conditions of Storage, and Changing p and find one of r of an inch in thickness to be 2 tures. ideal. We have obtained desirable results with Th O je of the Present invention is a new an extension in a single piece, preferably extendand improved electric blasting initietor- An ing lengthwise across the base of the plug, so that additional object is an electric blasting initiator t 1 t e dim i f th extension across which is readily adaptable to mechanical asthe base of t plug 111 approximate to the 25 Sem ly- Add o objects Will be apparent from diameter of the plug itself, the thickness of the the following detailed description of our invenextension across the base f the plug being io preciably less than the diameter of the plug itself W have found that these Objects are 31000111- and preferably being within the range noted in plished and t e foregoing disadvantages overthe foregoing. This extension arrangement is 30 co e by manufacturing e c c blasting initiodesirable in order to effect an absolutely waterto S according to the process of o invention, proof relationship between said leg wires and said whic Comprises molding and compressing a plug, especially in mass production. Likewise the ea ed material about the leg Wires of the elecextension is of particular advantage for rendertrio blasting init ator to fo m aresilient P ing the completed. initiator assembly resistant that e rubber-like Plug, and to form an exten' against any forces which would otherwise tend sion of t e am material-e8 Said P and of to pull the leg wires and plug from the shell. c a area of oroS,S-$eotio!1 beyond the base of In order to describe our invention more clearly, 531d P and integral therewith: Said reduced we shall refer to the attached drawing which 40 F p d closely adhermg to illustrates apreferred embodiment thereof. This 40 Sam leg F'g f provlgmgl it 5 1 is done solely by way of illustration and is not 3:23 ga gt g g g g x is; 5 to be regarded as a limitation upon the scope of -vulcanizable or thermoplastic material possessing our tnventlon f maily i g wlttnn the resilient properties, that is, any rubber-like mateggggg i g gigggfiggti art readfly a the term rubber-like we refer 0 those g g fg generally possessed by rubbetr Referring generally to the various figures of positions, namely, elasticity, springiness, extensithe drawing, 1 15 F Vertlcal Sectlon P the bility, and in one sense of the word, compressi- Preffm'ed F P reslhem g accordlng bi1ity As brought t 1 t on in our sDeciticaour invention. Fig. 2 15 an end view of said plug tion, this capacity of the plug material for r showing the extension thereon. Fig. 3 is a vertibounding, springing back and returning to its cal section of a complete electric blasting cap original shape without permanent deformation, assembly containing the resilient, rubber-like which is characteristic of rubber and similar plug of our invention. Figures 4, 5 and 6 are compounds, is effective in the plug of our insimilar views of slightly different embodiments of 55 the extension portion of the plug of our invention.

Similar characters are used throughout the several views and in the following description to designate corresponding parts.

Referring in greater detail to the drawing of the finished plug, the bare ends I4 of the leg wires are shown in Fig. 1 to be embedded in the tion referred to in the following. The bridge wire.

I6 connects the bare ends of the leg wires.

In Fig. 2 the general relative proportions of the area of the cross-section of the extension I5 and that of the bridge plug ,I'I, may be ob, served. The leg wires III are shown in position and are connected by the bridge wire I 6.

In Fig. 3 may be seen the location, of the resilient, that is, rubber-like bridge plug in the assembled electric blasting cap. The plug is crimped in place in the open end of the electric blasting cap shell 23, said closure being effected by means of the internal annular beads or grooves 24 in the shell wall, whereby the plug is gripped and held firmly in position. The bridge wire I6 is embedded in an ignition composition 20, below which is a priming composition 2] and a base charge 22. 1

In Figures 4, 5 and 6, the extension I5 is depicted in the form of a pyramid, a truncated cone, and separated extensions around each leg wire, respectively.

A detailed description of the preferred molding process of our invention is described in copending application Serial No. 244,334, filed Dec. 7, 1938.

After the desired molding period, the two sections of the mold are separated and the wires, enclosed in the rubber plug of preferred characteristics, are removed. Whereasany vulcanizable resilient material, that is, any material having springy, rubber-like properties including the so-called rubber substitutes, as well as varying degrees of vulcanized rubber may be employed for the formation of our improved plug, we prefer to use a crude rubber composition.

The finished bridge plug is then introduced into the open end of the charged electric blasting cap shell 23 and crimped into a water impervious relationship with said 'shell.

Our electric blasting initiator offers outstanding advantages over the art. By the development of an initiator wherein no waterproofing or sealing materials are necessary, we have eliminated the hazards inherent in the old process of pouring molten materials by hand into a loaded shell. In our invention, the bridge plug is simply crimped in place in the loaded shell, a step which may be readily mechanized, and carried out at normal temperatures. Furthermore, our assembly is an exceptionally strong one mechanically, thus permitting greater exposure security without damage to the blasting cap. Tests have demonstrated that blasting caps made by our invention are capable of consistently withstanding much higher water pressures than the ordinary type wherein waterproofing and sealing materials are emformed about the leg wires of said initiator, said plug having at its base an extension of the same material having a decreased area of cross-section with respect to that of the body of said plug and integral therewith, the material of said extension 0 surrounding and. closely adhering to said leg wires forming a Waterproof seal between said leg wires and plug, and a charged shell crimped about said plug in waterproof relationship therewith.

2. A water impervious electric blasting initiator adapted to mechanical assembly, which initiator comprises'a bridge plug of rubber-like material formed about the leg wires of said initiator, said plug having at its base an extension of the same material and integral with same plug such that the ratio of the area of cross-section of said extension to the combined area of cross section of the leg wires is small, the material of said extension surrounding and closely adhering to said leg wires forming a waterproof seal between said leg wires and plug, and a charged shell crimped about said plug in waterproof relationship therewith.

3. A waterimpervious electric blasting initiator adapted to mechanical assembly, which initiator comprises a bridge, plug of rubber-like material formed about the leg wires of said initiator, said plug having a reduced extension of the same material integral with its base, the material of said extension surrounding and closely adhering to said leg wires forming a waterproof seal between said leg wires and plug, and a charged shell crimped about said plug in waterproof relationship therewith.

4. A water impervious electric blasting initiator I adaptedto mechanica. assembly, which initiator comprises a bridge plug of rubber-like material formed about the leg wires of said initiator, said plug having at its base and integral therewith an extension such that the ratio of the area of crosssection of said extension to the combined area of cross-section of the leg wires is relatively small, the material of said extension surrounding and closely adhering to; said leg wires forming a waterproof seal between said leg wires and plug, and a charged shell crimped about said plug in waterproof relationship therewith.

5. A water impervious electric blasting initiator adapted to mechanical assembly, which comprises a bridge plug of rubber-like material vulcanized about the leg wires of said initiator, said plug having a reduced extension beyond its base and,

integral therewith, the material of said extension surrounding and closely adhering to said leg wires forming a waterproof seal between said leg wires and plug, and a charged shell crimped about said plug in waterproof relationship therewith.

. 6. A water impervious electric blasting initiator adapted to mechanical assembly, which comprises a bridge plug of rubber-like material vulcanized about the leg wires of said initiator, said plug having an extended portion of the same material at its base and integral therewith characterized by a cross-section, which does-not greatly exceed the cross-section of the leg wires, the material of said extended portion surrounding and closely adhering to said legwires to form a water-tight seal between the leg wires and the plug.

'7. A water impervious electric blasting initiator adaptable to mechanical assembly, which comprises a bridge plug of rubber-like material 

